Studies described in this proposal are designed to elucidate the pharmacology and enhance the therapeutic utility of the vinca alkaloids, vinblastine (VLB) and vincristine (VCR). Ussng techniques developed in this laboratory, we will prepare radiolabeled VLB and VCR of high purity and specific activity. These reagents will then be used to study the cellular pharmacology of the vinca alkaloids, with emphasis on identifying the mechanism of action and the means whereby cells develop resistance to these agents. Our studies will utilize cell lines both sensitive and resistant to the action of the alkaloids. We will: (1) Evaluate wether there is cross-resistance to VCR of a cell line which is 100-fold resistant to VLB; (2) Determine cellular uptake and washout kinetics of VLB and VCR in both cell lines, to evaluate for resistance factors, and determine the nature of transport into the cell and the pool size of bound and unbound drug; (3) Localize and quantitate the binding sites for the vincaswithin the cell; (4) Quantitate vinca binding with each intracellular component, determining association constants, where possible, and again comparing sensitive and resistant cell lines; (5) Search for improvements in recovery and separation techniques and in the use of the analytic tools, mass spectrometry and nuclear magnetic resonance to quantitative and sensitive enough levels to evaluate metabolite structures; (6) Study the metabolic fate of the vinca alkaloids, especially after the improvements in analytic technique in (5) have been developed.